The simple answer is: A seal that fits around the rear of the crankshaft to prevent oil leakage. The more in depth answer is: A rear main seal, also known as a main seal or rear main bearing seal is located between the engine and transmission. The crankshaft (the internal engine part that the pistons are connected to) sticks out of the rear of the engine, and the flywheel & transmission bolt to this crankshaft. The engine oil lubricates the crankshaft, pistons and other internal parts of the engine. The rear main seal is inserted into the back of the block and fits snuggly around the rear of the crankshaft and keeps the engine oil from escaping.

What are the symptoms of a rear main seal leak?

Depending on the severity of the leak the first thing you may notice is the oil level going down. The next thing that happens is spotting, where you will find oil spots, located on the driveway or garage. While looking under the vehicle around the area where the engine and transmission connect, you will find oil dripping, or a oil residue with dirt caked on this part of the vehicle. Most noticeably under the oil pan and the front of the transmission. In some transmissions, it will actually be the oil leaking out of the front of the transmission. In some manual transmission vehicles, you may also notice some slipping of the clutch, which can occur with a leaking rear main seal.

What causes the rear seal to leak?

The most common cause of rear seal leaks is age and/or high mileage. The seal can also leak due to the vehicle being stored for an extended period of time, or from running the engine low on oil. This causes drying and hardening of the seal leading to shrinking, cracking and tearing of the rear main seal.

What other factors can contribute to a rear main seal leak?

A few things can cause a rear main seal leak to worsen that is not the fault of the seal itself. If the oil level is too high (filled over the full mark) or the PVC (Positive Crankcase Ventilation) system is not functioning correctly, leaks can occur. The PVC system prevents pressure from building up inside the engine and if it fails, the pressure will cause the oil to leak out. It is a good idea to clean or replace the PCV valve regularly to prevent this problem.

Do I need to use Bar’s Leaks Rear Main Seal with every oil change?

No, we have found that you can receive good results if you reuse the product every other oil change.

How do you replace a rear main seal?

For most rear wheel drive vehicles the transmission is removed to replace the seal. On front wheel drive vehicles, it is usually easiest to remove the engine to gain access to replacing the seal. Either way, this is an expensive procedure.

What else can be done to stop a leaking rear seal other than replacement?

Bar’s Leaks Concentrated Rear Main Seal Repair is one of the only products of its kind on the market specifically designed to solve rear seal oil leaking problems. There are special oil additives on the market that are designed to swell the rubber of the rear seal and cause it to expand, thus sealing off the leak. You can also try using thicker weight engine oil, like 50 weight. The thicker oil can fill in the gap between the seal and the crankshaft, and could slow the leak down.

How does Bar’s Leaks Rear Main Seal Repair work?

This product works in two ways to help solve most any seal type leak. 1) The seal restorer additive restores seal size, flexibility and elasticity lost due to engine heat, age and high mileage. 2) The seal polymer works by building a polymeric film around the rear main seal and also filling in any groove worn into the crankshaft by the seal.

What types of seals will Bar’s Leaks Rear Main Seal Repair fix?

Because of the Bar’s Leaks 2X Action formula, the product has additives to work on any of the three types of rear main seals, no matter what the material.

Yes. Even though it is specially designed to seal rear main leaks, it also works better than a conventional stop leak on all other engine oil leaks. This includes the timing cover seal, cam seals, O-rings and other seals and gaskets.

Will Bar’s Leaks Rear Main Seal Repair clog my oil filter?

No. Unlike our cooling system products, Bar’s Leaks Rear Main Seal Repair has no particles to plug the leak. It contains special polymers and seal conditioners to stop seal leaks.

Bar’s Leaks is the leader that specializes in chemical solutions for rear main seal leaks and other automotive issues. Our products are effective and affordable. And they’re easy to use, too. If you know how to pop the hood on your car, you can install our rear oil seal solution. We design our products for ease of use, because a good solution isn’t very helpful to everyday drivers if they can’t use it. At Bar’s Leaks, we do everything we can to get you back on the road in good condition just as quickly as possible, by offering rear main seal leak products and much more.

Most rear main seal leaks are caused by a combination of normal wear in the crankshaft and seal combined with the drying, hardening and shrinking of the main seal. Bar’s Leaks Concentrated Rear Main Seal Repair restores the seal to like-new condition, and also contains additives to stop leaks in severely worn seals and crankshafts. Not to mention, it works with ALL gasoline and diesel engines using conventional, high mileage and synthetic oil. We’ve gone to great lengths to ensure that our rear oil seal solution is working for you in all possible ways. You can count on us for a rear main seal leak that takes care of your problems and helps prevent future leaking.

You can trust that our products are the fastest, safest way to get your show back on the road — we’ve been proving that since 1947.

Products to Fit Your Lifestyle and Budget

For nearly 70 years, the team at Bar’s Leaks has been working to serve everyday drivers just like you with affordable, easy-to-use, effective chemical repair solutions for a range of automotive problems. These solutions include our oil stop leak products, as well as solutions for cooling systems, head gaskets, power steering, transmissions and much more. While you’ll find plenty of options when searching for a rear oil seal product, you won’t find the same level of effectiveness you’ll get with Bar’s Leaks.

Our products are developed and manufactured in the United States, just an hour outside of Detroit. Our top-flight chemical engineers are always searching for ways to enchance our existing products and to develop new products in response to new automotive innovations and technologies. When you want the best rear main seal leak solution available, look no further than the track record of success at Bar’s Leaks.

Leave a Review

“This product saved me a lot of money. It made a good car into a really nice car. I'm really sold on the Bar's Leaks Real Main Seal repair, and I'll sure buy it again.”

J. Elder - Altanta, GA

“I don't normally do this, but I've found an AMERICAN company whose products actually work, and work WELL!!! So I had to write to thank you for your hard work and integrity in a world filled with automotive charlatans and snake-oil marketing.

Main seal leak stop saved my tractor. Oil leak stop saved my aging Subaru. Rislone keeps all my engines running clean and quiet, even with several hundred thousand miles! And Bar's Leaks has saved several radiators and heat exchangers. In a day and age where money does not go very far, your products help the average joe to keep a leg up, and repairs down, on a consistent basis!! I couldn't have kept three cars going through Northern Michigan's brutal seasons, while putting a kid through college without some help, and that came through in the form of several Bar's Products. Thank you folks, for your excellent products, and for keeping it simple, non-corporate, and integrity-based. Proud to be a fellow Michigander (Traverse City). Keep up the good work. You've got a devoted customer and free word-of-mouth advertising for life. -- Sincerely, Tim W.”

Timothy W. - Traverse City, MI

“I just rebuilt my 1966 442 400 cu.in. engine. I was apparently rusty on how to properly install the rear main seal (rope style) and it leaked almost from the get-go. I reluctantly put a quart of your product in my engine. I put over 100 miles on it and it still leaked. I was going to pull the engine and do it right at the end of the summer. Two days later I noticed there was no oil under the car when I pulled out of the garage. I couldn't believe it, the leak stopped. No oil anywhere under the car. Un-believeable.”

F. H. - Orland Park

“I have a 1985 Toyota Supra in mint condition; it has had an annoying small oil leak for over 10yrs now without finding a solution. I even tried engine oil stop leak from several companies without any luck. I saw your rear main seal conditioner and it was one that I never tried or heard of before so I tried it. WOW in less than 30 miles all the leaks stopped. Now with a total of 60 miles it still hasn't left any drops of oil on the garage floor. What a product. I will be adding it at every oil change from now on. Now my car is perfect once again. Thanks for coming up with such a GREAT product!”

D. B. - Fair Lawn

“I am now a big fan of your Rear Main Seal Repair. I have a 69 Firebird 400 conv. that I have practically owned since new. It is mostly all original with original drivetrain, interior and top. It has 105K miles and when I have taken it out of the garage it has left a trail of oil down the driveway. After using your product I was amazed that the leak stopped. I have used other products but nothing helped. I would be glad to endorse your product and if you are interested I can send you pictures of the car. Thanks for a great product.”

C. W. F. - Phoenix, AZ

“I have a 1966 Bronco that had a steady rear main leak. I changed the oil pan gasket in hopes this was the problem. I was going to change the rear main seal but it was a one piece type. This means the transmission has to come out to replace the rear main. I was very discouraged after performing this very large job only to find out I had the same problem. A buddy of mine recommended your product and I was a little hesitant of a product like this. To my surprise it worked after driving the vehicle for two day I had no leaks. I was so relieved that I wanted to take the time and thank you for such a great product. This saved me so much time and aggravation as I am a do it yourselfer.”

J. E. - Burlington, NC

“I am an amateur car collector and restorer (easy on the restoration). Recently I purchased a 1966 Ford Thunderbird, from the original owner. I drove it from Muncie IN. to New Mexico. After arriving home I started experiencing some problems with the car. Old cars have problems. The rear main seal was leaking. Before paying to have it replaced I used your Rear Main Seal restoration fluid. It worked perfectly! Then, I started getting water in the exhaust. Again, before paying for expensive repairs, I used your head gasket sealer. To my surprise it to worked perfectly! Your products have saved me hundreds of dollars in repairs. Just wanted to say thank you, and I will be recommending your products every chance I get.”

T. V. - Las Cruces, CA

“I have a 1993 Allante Northstar, engine had a oil leak. Cadillac wanted $3,800.00 to fix it so I put a quart of Rear Main Seal Repair in the crank case I think it stop 99%. How long do you think this will last or should I try the same thing again, I also have a 1966 Impala with a leak around the rear main should I trust my luck, hoping to here from you, I have used your product since the 50s keep up the good work an God bless all of you.”

R. F. C. - Denver, CO

“Hi my name is Paul I have a 1983 chaparal boat with a 120 hp io merc cruiser stern drive unit for power. Two weeks ago I noticed bad oil leak coming from the back of the motor. From where the leak was it looked like the oil pan was leaking, so my son and I went and put on a new oil pan gasket, the leak was still there. Not wanting to lose the whole boating season my father said I may want to try your Rear Main sealer. At this time I did not have $1800.00 dollars to repair it, so I tried your sealer. I ran the boat in my yard for about one half hour. I was disappointed as the leak was still there. I was losing a half a quart of oil in this short amount of time, after calling around again for repair prices I decided to try one more time. Being tired and mad I put the rpms from idle to 3000 and went into the house. after about forty minutes I went back out and I was shocked, I saw only a small amount in the drip pan. I could not believe what I saw! After checking the oil and measuring what was lost, I only lost a half of a cup of oil. I am very happy that repair in a bottle does work, Thank you for this product. I know that this is not a permanent fix but it looks like I will be able to use my boat for the rest of the summer season. I am hoping that my local parts store gets more in soon so I can have some on stand by. My son Ryan is a car repair tech and I told him to tell every one that this Rear Main sealer really works. Please do not stop making this product!”

P. W. J. - Wrightstown, NJ

“I don't usually put additives in my vehicles, but I just recently purchased an old 1984 f250 with a 460 engine with a rear main seal leak. I heard these 460 engines always have trouble with the main seals leaking on them and I didn't want to do a major repair on this vehicle because all I need this truck for is to help me and my wife move. So I heard about the Bars rear main seal additive working good for some people and so I decided what the heck and put it in this old truck. Well I was very surprised how well this stopped over 95% of my leak and it worked within 2 days. All I have is just a little bit of wetness on the trans. bell housing and it doesn't drip at all like it used to. I am very pleased with this product. It saved me from having to do all that work. I would definitely buy this product again. Thank you Bars.”

Documents

FAQ

What is a rear main seal?

The simple answer is: A seal that fits around the rear of the crankshaft to prevent oil leakage. The more in depth answer is: A rear main seal, also known as a main seal or rear main bearing seal is located between the engine and transmission. The crankshaft (the internal engine part that the pistons are connected to) sticks out of the rear of the engine, and the flywheel & transmission bolt to this crankshaft. The engine oil lubricates the crankshaft, pistons and other internal parts of the engine. The rear main seal is inserted into the back of the block and fits snuggly around the rear of the crankshaft and keeps the engine oil from escaping.

What are the symptoms of a rear main seal leak?

Depending on the severity of the leak the first thing you may notice is the oil level going down. The next thing that happens is spotting, where you will find oil spots, located on the driveway or garage. While looking under the vehicle around the area where the engine and transmission connect, you will find oil dripping, or a oil residue with dirt caked on this part of the vehicle. Most noticeably under the oil pan and the front of the transmission. In some transmissions, it will actually be the oil leaking out of the front of the transmission. In some manual transmission vehicles, you may also notice some slipping of the clutch, which can occur with a leaking rear main seal.

What causes the rear seal to leak?

The most common cause of rear seal leaks is age and/or high mileage. The seal can also leak due to the vehicle being stored for an extended period of time, or from running the engine low on oil. This causes drying and hardening of the seal leading to shrinking, cracking and tearing of the rear main seal.

What other factors can contribute to a rear main seal leak?

A few things can cause a rear main seal leak to worsen that is not the fault of the seal itself. If the oil level is too high (filled over the full mark) or the PVC (Positive Crankcase Ventilation) system is not functioning correctly, leaks can occur. The PVC system prevents pressure from building up inside the engine and if it fails, the pressure will cause the oil to leak out. It is a good idea to clean or replace the PCV valve regularly to prevent this problem.

Do I need to use Bar’s Leaks Rear Main Seal with every oil change?

No, we have found that you can receive good results if you reuse the product every other oil change.

How do you replace a rear main seal?

For most rear wheel drive vehicles the transmission is removed to replace the seal. On front wheel drive vehicles, it is usually easiest to remove the engine to gain access to replacing the seal. Either way, this is an expensive procedure.

What else can be done to stop a leaking rear seal other than replacement?

Bar’s Leaks Concentrated Rear Main Seal Repair is one of the only products of its kind on the market specifically designed to solve rear seal oil leaking problems. There are special oil additives on the market that are designed to swell the rubber of the rear seal and cause it to expand, thus sealing off the leak. You can also try using thicker weight engine oil, like 50 weight. The thicker oil can fill in the gap between the seal and the crankshaft, and could slow the leak down.

How does Bar’s Leaks Rear Main Seal Repair work?

This product works in two ways to help solve most any seal type leak. 1) The seal restorer additive restores seal size, flexibility and elasticity lost due to engine heat, age and high mileage. 2) The seal polymer works by building a polymeric film around the rear main seal and also filling in any groove worn into the crankshaft by the seal.

What types of seals will Bar’s Leaks Rear Main Seal Repair fix?

Because of the Bar’s Leaks 2X Action formula, the product has additives to work on any of the three types of rear main seals, no matter what the material.

Yes. Even though it is specially designed to seal rear main leaks, it also works better than a conventional stop leak on all other engine oil leaks. This includes the timing cover seal, cam seals, O-rings and other seals and gaskets.

Will Bar’s Leaks Rear Main Seal Repair clog my oil filter?

No. Unlike our cooling system products, Bar’s Leaks Rear Main Seal Repair has no particles to plug the leak. It contains special polymers and seal conditioners to stop seal leaks.